Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or grease with vegetable oil.

In a mixing bowl, whisk together the milk, vegetable oil, egg, and vanilla extract until well combined.

In another bowl, combine the flour, sugar, baking powder, and salt. Stir until well mixed.

Slowly add the dry mixture to the wet mixture, gently folding them together. Be careful not to over-mix.

Fold in the blueberries, being cautious to avoid breaking them.

In a separate bowl, mix the brown sugar, flour, cinnamon, and cold butter until crumbs form.

Pour the muffin batter into the prepared muffin tin until each cup is about two-thirds full.

Sprinkle the streusel topping generously over each muffin.

Bake for 20-25 minutes or until a toothpick inserted in the center comes out clean.

Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack.